In 3G UMTS communication systems, significant time is required for mobile stations, or subscriber devices, to search for neighbor pilot signals from neighbor list information provided by network base stations in a system information broadcast or similar message.
Presently, when searching for neighbor pilot signals, UMTS frame synchronization and scrambling code identification procedures are performed at separate signal processing stages, which generally require operation of the radio frequency (RF) receiver for extended time periods, including operation during standby mode, which represents more than an insubstantial drain on the battery.
At Stage 1 signal processing, slot boundaries of the primary synchronization channel (PSCH) of received neighbor signals are determined. Subsequently, at the Stage 2 processing, frame synchronization is performed by correlating several slots of the secondary synchronization channel (SSCH) with each of 16 secondary synchronization codes (SSC), thus permitting frame boundary determination and Group Code identification, from which a corresponding set of scrambling codes may be determined. In theory, assuming no noise or fading, frame synchronization requires correlation over at least 3 slots, but in practice the correlation may occur over 15 or more slots. Frame synchronization must be performed for each slot boundary identified at Stage 1 processing. At Stage 3 processing, base station selection occurs based upon the scrambling codes identified in Stage 2.
The existing frame synchronization procedure produces many false results and has a low detection probability, partly because the SSCH channel is a weak signal. Also, since the SSCH channel may be correlated only for 256 chips per slot, correlation over multiple slots is usually required, thus prolonging the time during which the RF receiver must operate. The existing frame synchronization process is thus relatively inefficient, particularly during standby mode operation when the RF receiver would otherwise be inoperative.
The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description of the Disclosure and the accompanying drawings described below.